The present invention is directed to detectable polymers and methods for detecting polymers in aqueous systems. In particular, the present invention concerns water-soluble polymers containing a pendant amine group capable of reacting with amine-reactive labels.
Water-soluble polymers are used in many aqueous systems, for example, as mineral dispersants, as water-treatment additives for boiler waters, cooling towers, reverse osmosis applications, sugar refining, paper production, geothermal processes and oil wells, and as detergent additives acting as builders, anti-filming agents, dispersants, sequestering agents and encrustation inhibitors. In many of these aqueous systems it is desirable to know the level of polymer in the system. However, the level of active polymer is not simply a function of how much polymer has been added. The polymer may have adhered to a surface or may have flocculated out with sediment, or the polymer itself may have decomposed. Because polymers generally add cost to processes employing them, it is desirable to be able to use them efficiently.
One of the problems associated with detecting polymers in aqueous systems is that the polymers are generally present at very low levels, from 500 down to less than 5 parts per million (ppm). Another problem associated with detecting polymers in aqueous solutions is that the detection methods frequently lack selectivity and may give false results for components of the aqueous system other than polymers.
One attempt at overcoming these problems has been to use, in conjunction with the polymer, a tracer compound. The assumption behind this approach is that the tracer compound will be present in the aqueous system at a level proportional to the level of the polymer. However, this assumption is undermined by the fact that the fate of the tracer compound and the fate of the polymer in the aqueous system may differ.
Another approach to overcoming these problems is to incorporate into the polymer a detectable moiety. This has been accomplished, for example, by using a fluorescent monomer in preparing the polymer. This approach has the drawback of additional processing steps in preparing the fluorescent monomer. Also, the presence of the fluorescent moiety, which is usually a fairly bulky, hydrophilic group, may interfere with the performance characteristics of the resulting polymer. For example, many water treatment polymers have molecular weights below 10,000; the attachment of a fluorescent moiety can be a significant percentage of that, which can affect the function of the polymer.
U.S. Pat. No. 5,171,450 attempted to overcome these problems by recognizing that amine-containing dyes and amine-containing fluorescent compounds can be used with conventional water-treatment polymers which contain functional groups of carboxylic acids or amides. The amine-containing dyes or fluorescent compounds can be attached to these polymers via a transamidation reaction to create labeled or "tagged" polymers. These tagged polymers can be used and detected in aqueous systems. The drawbacks to this approach are that (1) the attachment of the fluorescent label may not be quantitative and (2) the presence of the label may interfere with the functioning of the polymer in the aqueous system.
The present invention overcomes the above problems by providing on the polymer not a detectable label but instead a site for the attachment of one, the label being attached during a reaction involving just a sample of the polymer removed for analysis. In this way the label is never attached to any polymer actually residing in the aqueous system in which it is being used.